Air Con hissing

[old boy walters]

Hello,

I have a 97 A4 Avant which i noticed was hissing when i switched the engine off, which then dies down after about a minute. On closer inspection it seems to be coming from the air con pipes between the engine and bulkhead. I cant tell if it does this while the engine is on because of the noise of the engine. i am pretty sure it must be air con related as if i switch the air con before i end a journey there is no hissing when i cut the engine.

can anyone shed any light on whether this is normal or not ? if not normal any clues to what might be wrong.

any info much appreciated.

old boy w

[audimad]

Its normal, do not worry. As long as its still working don't panic

[jsmithee]

thank heavens for that, i've just had mine regassed and it's doing the exact same thing, i thought all my precious r134 was leaking

[karachi_kops]

h i audimad

cheers for the post .. msot reassuring its nothing to worry about. the hissing noise has made me not use the air con!

how often should the air con be regassed? i know it depends on usage ... but should i be looking at regassing ever year?

[pologt]

Hi, I know this is an old post but having just topped up my air con I have the same problem - a loud hiss near the battery when the engine is turned off.

The top up seems to have fixed my air con but I am concerned that I have put too much gas in and burst a pipe or connection.

The hoses near the battery seem slightly corroded (possibly due to the acid) so it would not surprise me if one has punctured.

If this is normal (as suggested) what is causing the noise?

Many thanks for any advice!

[au_sjo]

My recently acquired '98 1.8 Avant also shows the same behaviour. I am under the assumption that the gas is a bit low as the a/c isn't particularly effective, but as above when you key off it hisses for 20-30 seconds or so.

On another note, my a/c compressor ticks and is fairly noisy. I suspect this is a sign of impending doom. It appears to have had a replacement pulley/clutch on the compressor at some point in the not so distant past and a friend of mine at Audi said they have a habit of 'falling off'.

Common?

[pologt]

Not sure about your gas levels... mine only started the hissing after I topped it up... unless we both have major leaks that would imply your levels are ok???

I have read in other places that the hissing is normal and is the liquid turning back into a gas when the air con is shut off.

I think only the centre vents are cooled so make sure they are open (not the outside ones).

Don't know about the pulley but it wouldn't surprise me... the belt arrangement at the front is tricky and looks difficult to maintain (so probably isn't).

[au_sjo]

I have read in other places that the hissing is normal and is the liquid turning back into a gas when the air con is shut off.

Yeah but in all fairness, they don't do it from new. If the behavious of something changes over time then there must be a cause of it

[kmm]

Hi, i,ve recently bought a '98 S4 and it hisses when i turn off the engine too. My air-con work perfectly and is nice and cold. It's either normal for the cars to do this or our air-cons are about to pack in. Next time i take it for a run, i'll leave my air-con off and see if it hisses once turned off.

[Tavli]

I belive it is just the gas recirculating back into to the chamber, mine also does it, also if you have been using the aircon for some time on a decent run take a look under the car after about 10 mins and you will see a pool of water, this worried me when I first noticed it but this is also normal.